The invention relates the production of a polymer in a gas phase, fluidized bed polymerization. More particularly, the invention relates to a sampling system for such a gas phase polymerization of a polymer (such as PE, PP, and/or a sticky polymer such as an EPR).
The physical and chemical properties of the product being produced in a continuous gas phase reactor with a fluidized bed must be determined to ensure the product remains within specification. Ideally, these properties should be measured in-situ, but reliable technology has not been developed to accomplish this goal. Therefore, product samples need to be taken and analyzed externally to the reactor. Generally such samples are taken in conveying lines after the reactor.
When this is done, some time lag is introduced depending on the equipment between the reactor and the sample point and the residence times in that equipment. Taking samples from conveying lines or downstream of pressure-rated product discharge tanks has been the norm.
Cyclones have been used to separate the conveying gas from the solids. These systems work reasonably well for polymers (e.g., crystalline alpha olefin polymers) where the monomers are not too hazardous and can be easily purged. (Cyclones would probably not work well for sticky polymers)
However, the advent of gas-phase processes for sticky polymers such as ethylene-propylene rubbers (EPR), including ethylenepropylene-diene elastomers, and butadiene rubbers (BR) makes these simple samples systems useless due to the hazard ratings of the monomer (i.e., the diene). EPR products contain (ethyldiene norbornene (ENB) and BR products contain 1,3-butadiene which have stringent controls to limit air emissions and human exposure. ENB has a strong odor which can be detected in ambient air at 13 ppbv. The current exposure limit for 1,3-butadiene is only 1 ppmv.
Accordingly, there is an on going need to obtain safe, reliable sampling of such polymerizations.
Surprisingly, the present invention provides a process and apparatus for sampling during the polymerization of a sticky polymer.
There is provided a process for sampling a polymer during its production in a gas phase fluidized bed reactor comprising:
(1) analyzing a sample containment vessel for leaks from the sample containment vessel to the environment and for leaks from the reactor to the sample containment vessel;
(2) removing a sample of polymer from the fluidized bed to the sample containment vessel;
(3) contacting the sample of polymer with an aluminum alkyl quenching agent;
(4) purging the sample of polymer in the sample containment vessel with an inert gas; and
(5) discharging said sample of polymer from the sample containment vessel.
There is further provided an apparatus comprising:
(1) a pressure rated sampling vessel with a conical discharge bottom wherein the cone angle is sufficiently steep to prevent sticky solids from easily bridging the bottom of the vessel;
(2) one or more filters to keep a solid product inside the sampling vessel and prevent it from migrating to instrumentation or to other process streams;
(3) a programmable logic controller (PLC) which can sequence the operation of the valves and perform logic tests in conjunction with other process instrumentation including pressure, temperature, and flow sensors ensuring the sampling system is operating safely and is performing the desired functions;
(4) one or more full-bore PLC-controlled remotely actuated valves connected to the reactor with metal seats that minimize leaks from the reactor into the sampling vessel;
(5) one or more PLC-controlled remotely actuated valves connected the sampling vessel to other process streams such as purge gas, quench agent, vent, flare, reactor cycle gas, or to discharge the product; and
(6) a manual discharge isolation valve allowing control of the final discharge of the product into the sample container for off-line analysis.